Freezing the orientation of a nematic stretched elastomer by photocrosslinking

In this paper we tried to prepare shape memory main chain LC materials, by photopolymerizing (UV-curing) LC elastomers subjected to uniaxial stress. For this purpose, we prepared blends, having different compositions, of a well-known mesogenic diglycidyl-terminated monomer, namely 4,4′-diglycidyloxybiphenyl (DIF), with its homologous bearing lateral photocurable allyl groups (AllDIF). The obtained blends were thermally cured with an aliphatic diacid (decandioic acid, SA), and gave LC networks in all the cases but 100% AllDIF composition. LC networks corresponding to a selected blend composition were subsequently conditioned with a radical photoinitiator, namely 2-hydroxy-2-methyl-1-phenyl propan-1-one and photocrosslinked by UV-curing either as such or while subjected to uniaxial stress. The characteristics of the resulting networks were investigated by means of DSC, XRD, POM, FT-IR, DMTA, and TMA analyses. The effect of UV-curing under stretching and of photoinitiator uptake on the LC phase stability and on the orientation of the networks, as well as on their dynamic-mechanical and thermomechanical response are discussed.